WiiUtils: Add an online updater

While setting up a proper NAND for Wii emulation has become much easier
now that disc and online system updates work, they still require users
to have a recent disc game, certificates extracted from IOS or a NAND
dump for online updates to work and to really get all system titles.

This commit adds the ability to do an online update right from
Dolphin itself, which solves that usability issue.

Source/Core/Core/WiiUtils.h

@@ -4,11 +4,37 @@
 
 #pragma once
 
+#include <cstddef>
+#include <functional>
 #include <string>
 
+#include "Common/CommonTypes.h"
+
 // Small utility functions for common Wii related tasks.
 
 namespace WiiUtils
 {
 bool InstallWAD(const std::string& wad_path);
+
+enum class UpdateResult
+{
+  Succeeded,
+  AlreadyUpToDate,
+
+  // NUS errors and failures.
+  ServerFailed,
+  // General download failures.
+  DownloadFailed,
+  // Import failures.
+  ImportFailed,
+  // Update was cancelled.
+  Cancelled,
+};
+
+// Return false to cancel the update as soon as the current title has finished updating.
+using UpdateCallback = std::function<bool(size_t processed, size_t total, u64 title_id)>;
+// Download and install the latest version of all titles (if missing) from NUS.
+// If no region is specified, the region of the installed System Menu will be used.
+// If no region is specified and no system menu is installed, the update will fail.
+UpdateResult DoOnlineUpdate(UpdateCallback update_callback, const std::string& region);
 }